A monitoring device for at least one current pickup of a conveyor truck in a conveyor system is known from DE-GM 82 11 804. Underneath several parallel sliding contacts a transversely running shaft is arranged with entrainment means for each sliding contact, which in the case of a worn-out current pickup is actuated by a thereto assigned trigger. On the shaft, a cam disk is mounted which actuates a fixed switch. A prestressed spring restores the shaft with its entrainment means and the cam disk to their initial monitoring position. The drawback is that, on the one hand this mechanical monitoring device is of a relatively complicated construction, and, on the other hand, it does not work with precision, particularly in the case of sliding contacts, where the differences in height between new and used ones are relatively small. Besides, it has to be taken into account that due to the tolerances of the conveyor truck in operation, particularly under load, such a contact is actuated sometimes too early and other times too late and this way a safe monitoring of the state of the current collectors is not possible.
It is the object of the present invention to improve the monitoring device of the above-described type.